Infrared camera tube



March 15, 1960 R. w. REIDINGTON ETAL 2,928,971

INFRARED CAMERA TUBE Filed Dec. 20, 1957 2 Sheets-Sheet 1 /m/em0rs: 3 Row/0nd W Red/ng/on; P/fer J. van Heerden,

QJ M Their Attorney,

March 15, 1960 R. w. REDINGTON ET AL 2,928,971

INFRARED CAMERA TUBE 2 Sheets-Sheet 2 Filed Dec. 20. 1957 /n ventors. Row/0nd W. Recflhg/on; P/efer J. van Heera'en,

by y

. The/r Attorney.

n cArvmaA roan Application December 20, 1957, Serial No. 704,056

9 Claims. (Cl. 313-78) The present invention relates to an infrared camera tube and more particularly to a deflection and focusing system therefor.

In conventional vidicon-type camera tubes, a cathode electrode generates an electron beam that is focused on and deflected over the area of a photocond'ucting element or target upon which a scene is imaged. The heated cathode electrode produces infrared rays that although incident upon the target, do not affect the output signal because the target is insensitive to these rays. However, in an infrared camera tube the target is, of course, sensitive to infrared rays and thus should be shielded from the infrared rays from the cathode.

Accordingly, an object of the present invention is to provide an infrared camera tube in which no significant amount of infrared radiation from the cathode structure is incident upon the target.

Due to their straight line movement, infrared rays from the cathode structure can be prevented from reaching the target if the path between the cathode and target for these rays is circuitous. Of course, then a system is required that can deflect and focus an electron beam over a circuitous path.

Therefore, another object is to provide a system for deflecting and focusing an electron beam over a circuitous ath. p Either a magnetic system or an electrostatic system can be used to deflect and focus an electron beam. If both types of systems are suitable for a particular application, an electrostatic system is preferred because it is usually lighter, smaller, and requires less power than a magnetic system.

Thus, another object of the present invention is to provide an electrostatic system for deflecting and focusing an electron beam over a circuitous path.

In conventional electrostatic deflection and focusing systems, the electron beam strikes the target orthogonally only at the center with the result that more beam voltage is required to strike the outer portions of the target than the inner portions near the center. As a consequence, in low beam voltage acceleration systems often there is not suflicient voltage to cause the beam to strike all portions of the target with full intensity. Hence, a potential difference is established across the surface of the target that distorts the output signal. Another limitation of conventional electrostatic systems is that they produce considerable aberration and deflection defocusing.

.Hence, a further object is to provide an electrostatic deflection and focusing system in which the electron beam strikes the target orthogonally at all points thereof.

Still another object is to provide an improved electrostatic deflection and focusing system having low aberration and deflection defocusing. I, These and other objects are achieved by one form of ou'iiinvention in which fourconducting hemispherical defllectionelectrodes are utilized in concentric pairs to defflect an electronjbeam. The pairs ofelectrodes are positioned' in opposing relationship such that the electron 2,92,97l Patented Mar. 15, 1960 beam passes first between one pair of electrodes which provide horizontal deflection of the beam and then between the other pair of electrodes which provide vertical deflection. Both pairs of electrodes are blackened to absorb the infrared radiation from the cathode structure that produces the electron beam.

The novel features that we believe are characteristic of our invention are set forth in the appended claims. Our invention itself, together with further objects and advantages thereof may best be understood by reference to the following description taken in connection with the accompanying drawing, in which:

Fig. l is a sectional view of a pair of concentric sperical segment deflection electrodes,

Fig. 2 is a cross-sectional view of the electrodes of Fig. 1 taken along the lines 22,

Fig. 3 is a perspective view of a portion of one infrared camera tube embodiment in which hemispherically-shaped deflection electrodes are utilized,

Fig. 4 is a central sectional view of Fig. 3 with one pair of deflection electrodes rotated Fig. 5 is a side view, partly in section, of an infrared camera tube in which hemispherically-shaped deflection electrodes are utilized,

Fig. 6 is a perspective view of a portion of another infrared camera tube'embodiment in which pairs of quartor-sphere deflection electrodes are utilized,

Fig. 7 is a central sectional view of Fig. 6 with one pair of deflection electrodes rotated 90,

Fig. 8 is a side view, partly in section, of an infrared camera tube in which quarter-sphere deflection electrodes are utilized, and i Fig. 9 is a perspective view of a plurality of pairs of concentric spherical segment deflection electrodes in which a vertical section is taken through the first two pairs of electrodes and a horizontal section is taken through the last two pairs of electrodes.

In the several figures of the drawings, corresponding elements have been indicated by corresponding reference numerals to facilitate comparison. Referring now specifically to Fig. l, we have illustrated two spherical segment deflection electrodes 11 and 13, that are concentric at point 15 and that subtend the same solid angle. The shapes of these electrodes are better illustrated in the cross-sectional view of Fig. 2. If a voltage is ape plied between electrodes 11 and 13, the resulting spherical electric field deflects and focuses an electron beam from a point source 21 to an image point along a line extending from the point source 21 through the center 15 of the spherical electrodes. The exact position of this image, which depends upon the voltages applied to electrodes 11 and 13 and the sizes of these electrodes, is at the intersection of a line drawn tangent to the exit path of the electron beam from electrodes 11 and 13 and the line through point source 21 and center 15. This construction is valid regardless of whether the image is virtual or real. The voltage between deflection electrodes 11 and 13 may be such that the electron beam follows a circular path between these electrodes, in which case the point source 21 images at point 23. For any other voltage the path is elliptical'and thus point source 21 images at another point, e.g., point 25', It is to be noted that the image plane, which is indicated by a line 26 extending through points 23 and 25, is not orthogonal to the electron beam. I

What has been stated in reference to the electric field between small spherical segment electrodes is also true for spherical fields between larger electrodes such as hemispherical electrodes. In Fig. 3 we illustrate a portion of an infrared camera tube utilizing hemispherically' shaped deflection electrodes positioned to produce 'a deflection of the electron beam very similar to the'deflec .the beam in electron gun 27 and the center point 15.

An electrode 33 having a'line slit 35 extending along the portion of this line upon which the beam is focused and deflected provides a baffle for preventing infrared radiation from electron gun 27 from passing further into the system. It also reduces distortion from fringing fields at the edges of electrodes 29 and 31, and can be used to control astigmatism. To further eliminate the infrared radiation from electron gun 27, the interior of electrode 31 and the exterior of electrode 29 are blackened with a substance 36 such as lamp black that readily absorbs infrared radiation.

The electron beam 28 after passing through slit 35 enters the region between inner-hemispherical electrode 37 and outer-hemispherical electrode 39 which electrodes are concentrically mounted and are oppositely disposed with respect to electrodes 29 and 3-1 so that the beam paths in the two pairs of electrodes are orthogonal. To be more specific, the two pairs of electrodes are positioned such that there is a bisecting plane for electrodes 29 and 31 and a bisecting plane for electrodes 37 and 39 that intersect orthogonally along, a line that passes through the center of slit 35, or in other words midway between the electrodes of both pairs. At the exit region for the electron beam 23 from electrodes 37 and 3? a target 41 is placed to cover the area over which the electron beam 28 is deflected. A screen electrode 43 may be placed in front of target 31 to provide a homogeneous electric field in the immediate vicinity of target 41. The interior of electrode 3? and the exterior of electrode 37 may be blackened with lamp black or the like to absorb any infrared radiation that passes through slit 35.

The two pairs of deflection electrodes, although shown to be similar, may be different in size. Of course, if they are the same size, and with the same magnitude of deflection voltages applied on both pairs of electrodes, the electron beam is deflected over an approximately square area, which is often desired. If different sized pairs of electrodes are used, the magnitude of deflection voltages on the two pairs of electrodes must be different to produce a square area deflection.

As should be apparent, deflection voltages applied between electrodes 29 and 31 deflect beam 28 in a horizontal direction while those applied between electrodes 37 and 39 deflect beam 28 in a vertical direction. In other words beam 23 is deflected in two orthogonal directions by voltages applied to the two pairs of deflection electrodes. The exact manner in which area coverage is obtained by deflecting an electron beam in two orthogonal directions is the same as in oscilloscopes wherein flat rather than spherical deflection electrodes are used. However, the operating voltages for spherical segment deflection electrodes are quite diflerent than those for flat deflection electrodes. The deflection voltages applied to flat deflection electrodes are usually balanced so that it the voltages on one electrode of a pair rises, say volts, the voltage on the other electrode of this same pair lowers 10 volts. To produce the same effect upon the electron beam with spherical segment deflection electrodes the alternating voltages on the spherical segment deflection electrodes must vary inversely with the ratio of the radii of the spherical segments, and the direct voltages must vary inversely wtih the squares of those radii when the electron beam is injected midway between the electrodes 29 and 51. For examp e, assume t at the radius of electrode as is only 4 half that of electrode 31 so that the ratio of radii is 2 to 1. Then the deflection voltages applied to these electrodes must vary inversely or in other words the alternating current voltage applied to electrode 29 must be twice as great as that applied to electrode 31, and the direct voltage must be four times as great. The proper beam voltage is related to the direct voltages and the radii of the electrodes and in a camera'with similar pairs of electrodes should be made equal to the dilference in direct voltages on the electrodes of a pair times the product of the radii of the electrodes divided by the diiference in the squares of the radii. To illustrate suitable operating voltages for the hemispherical electrodes, if the inner electrodes have a radius of 1 /4 inches and the outer electrodes a radius of 2 inches and with a beam energy of 220 volts, suitable direct voltages for the inner and outer electrodes of both pairs of electrodes are 440 volts and 110 volts respectively. Suitable deflection voltages are approximately 60 volts peak on the inner hemispheres and approximately 30 volts peak on the outer hemispheres. With these voltages a target of slightly more than 2 centimeters in diameter may be scanned with a resolution of 0.1 to 0.2 millimeters.

In Fig. 4 we have illustrated a sectional view of Fig. 3 that for hemispheres 29 and 31 is taken through a horizontal bisecting plane and for hemispheres 37 and 39 is taken through a vertical biseoting plane. For convenience of illustration the vertical section for hemispheres 37 and 32' has been rotated to place it in a horizontal plane with the section for hemispheres 29 and 31. Electron gun 27 is seen to comprise a cathode 45 maintained at a suitable potential by a voltage applied to terminal 47, which cathode is heated by a heating element 49 energized at terminals 51. The electrons generated by cathode 45 are initially accelerated by a first electrode 53, which is maintained at a suitable operating potential by a voltage applied at terminal 55, and further accelerated by a second grid electrode 57 which is energized at terminal '59. The electrons are then focused approximately to a point by a lens system including a focusing electrode 60, which has an input terminal 62, and another electrode 63 that is maintained at the potential of the second grid electrode by means of an interconnecting lead 64. Thus, the electron beam at the edges of hemispherical plates 29 and 31 can be considered to be from a point source.

As previously explained, this point source images to a point where the electron beam intersects the line determined by the point source and the center 15 of the hemispheres 29 and 3-1. Deflection voltages applied to terminals 65 and 67 produce a varying electric field between plates 29 and 3-1 that deflects beam 28 in a horizontal direction along the slit 35 in electrode 33, which electrode is energized by a controllable voltage applied at terminal 69. Then the beam p-sses between plates 37 and 39 where it is deflected in a vertical direction by an electric field resulting from varying voltages applied through terminals 71 and 73 to plates 37 and 39, respectively. And, lastly it passes through screen electrode 43, which has an input terminal 75, to be imaged to a point on target 41.

Target 41 comprises a layer 77 of photoconduetive material such as germanium or silicon suitably doped with impurities such as gold, copper, cobalt, etc., that is coated on the rear with a conductor film 79. The number of electrons from the beam passing through material 77 to film 79 at any point thereof depends upon the amount of infrared radiation at that point. Also, as the electron beam 23 deflects past this point the number of the electrons from the beam incident thereon depends upon the number of electrons hat have leaked thro gh ma erial Consequen y, the number or e ser ns sudd n y nc de t upo h p nt of target 4. dep pon the rad a on at he respecti e ppiu s- The flow of electrons to these Points causes, by capadfi?! action, a corresponding flow of electrons from film 79 to ground through a resistor 80 across which a voltage is thus developed that is a time function of the intensity of the infrared radiation over substantially all the points of surface 43. An amplifier may be connected to terminal 81 to amplify the voltage across resistor 89 to a suitable magnitude so that it can be used to produce a visible signal of the infrared scene as for example, in the manner that a televised electrical signal is converted into a visible image.

Additional details of the infrared camera tube utilizing the hemispherical electrodes of Figs. 3 and 4 is illustrated in Fig. 5 in which an envelope 83 provides a vacuum seal for the deflection structure. At the bottom portion of envelope 83 an infrared ray transmitting window 85 is placed to transmit the infrared ray scene which is imaged on target 41 by a lens 87. Suitable insulators 91 may be used to insulate conductors connected to the various components of the deflection and focusing components.

Smaller spherical segments than hemispheres may be advantageously employed in infrared camera tubes for preventing infrared radiation from reaching the target while at the same time providing deflection and focusing of the electron beam. in Fig. 6 we illustrate the use of quarter-sphere segments in which the deflection and focusing system comprises two concentric quarter-spheres 93 and 95 that provide horizontal deflection and two other quarter-spheres 97 and 99 that provide vertical deflection of beam 28 so that it deflects over a large portion of target 41. Although the paths of the beam are not quite so circuitous as in the hemispherical embodiment, yet infrared radiation from electron gun 27 must reflect a number of times from the blackened walls of the quarter-spheres to reach target 41, and thus is greatly diminished. For reasons previously mentioned in the discussion of the hemispherical embodiment, the pairs of quarter-sphere electrodes need not be the same size.

In Fig. 7 we have illustrated a sectional view of Fig. 6 comprising a vertical bisecting section of quarter-spheres 93 and 95 and a vertical bisecting section of quarterspheres 97 and 99, both vertical sections being placed in a single plane to simplify illustration. As can be seen from this figure, one principal difference between the quarter-sphere embodiment and the hemisphere embodiment is that the beam 28 is not focused to a point as it leaves the first pair of quarter-spheres 93 and 95. This is because the exit region from these electrodes is not along a line extending from the point source of electron gun 27 through the center of these electrodes. However, the beam 28 is focused to a point where it leaves quarterspheres 97 and 99. The reason for the point image there can be understood if the two quarter-spheres are considered to be from a single hemisphere, the bottom portion of which has been rotated around 90.

In Fig. 8 we have illustrated the quarter-sphere embodiment in a vacuum envelope 83. The principal advantage of this embodiment, as is evident from this fig-' me, is its smallness as compared to the hemisphere embodiment. However, in the quarter-sphere embodiment the image plane is not orthogonal to the beam as it was with the hemispherical embodiment but rather is tipped slightly. This is not disadvantageous for infrared camera tube applications if a sufficiently high beam accelerating voltage is used but if the deflecting electrodes are utilized in a system in which the electron beam produces an image, as in television receivers, the resulting image is slightly distorted unless correcting voltages are applied to the deflection electrodes. This distortion, which is called keystoning, results from the tipped image plane causing the electron beam to travel a longer distance to some points of the image plane than to others. Since the amount of deflection of the electron beam is a function of the length of its path, the beam is deflected more when it travels the longer paths than when it travels the shorter paths, even though the deflection voltages are the" same in both instances. This distortion can be corrected quite simply by producing a counter distortion of the deflecting voltages.

In some deflection and focusing applications it may be desired to use small spherical segment electrodes.- such as those illustrated in Fig. 1 while obtaining an image;

Fig. 1. To eliminate this tipping another pair of de i: flection electrodes 113 and are mounted in opposing relationship such that the ends of the center lines of the spaces between the electrodes of both pairs, which are the lines along which beam 28 travels, are adjacent-. Thus, if the first pair of electrodes 1&1 and 103 tip the image plane downward, the second pair of electrodes 113 and 115 tip the image plane upward. Consequently,. if both pairs of electrodes are the same size and the alternating current deflection voltages on the pairs of electrodes are of the same magnitude but of opposite polarity, so that the two deflection voltages do not have an opposing effect, the tipping effects of both pairsof electrodes cancel and thus the image plane for the electron beam 28 as it leaves electrodes 113 and 115 is orthog' onal to the beam. If horizontal deflection is also de sired, two additional opposed pairs of electrodes 123, I25 and 135, 137 can be placed at right angles to the vertical deflection electrodes to produce horizontal deflection of the beam without tipping the image plane. This deflection and focusing system of Fig. 9 is obviously not very suitable for infrared camera applications because" the path for the electron beam is not circuitous. How-' ever, it is suited for other deflection and focusing applications such as in television picture tubes, camera tubes, oscilloscopes, etc. i I

From the above it is seen that an infrared camera tube has been provided in which very little infrared radiation from the electron gun reaches the target. Specifically, through the use of hemispherical or quarter-spherical deflection electrodes the beam can be made to follow a' circuitous path, which, if the electrodes are coated with lampblacl; or the like, results in a severe reduction of the amount of infrared radiation from the electron gun being incident upon the target. Further, the deflection;

electrodes are lighter and smaller and require less power than does a magnetic deflection system. And since the interaction region between the electrodes and the beam is long, only relatively weak fields and thus small deflec tion voltages are required. With small deflection voltages the fringing fields are correspondingly less important and consequently there is low aberration and deflection defocusing. I

In all of our figures we have illustrated the spherical segments as subtending the same solid angle. Although desired, this is not absolutely necessary,'for these seg-' ments need produce a spherical electric field only inthe immediate vicinity of the beam which, of course, can be, obtained even though the segments do not subtend the skilledin the art without departing from the spirit of our invention. We intend, therefore, by the appended claims, to: cover all such modifications and changesas fall within the true spirit and scope of our invention.

What we claim as new and desire to secure by Letters has a point approximately midway between the elec-.

trodes of each pair.

2.. An infrared camera tube comprising the deflection and focusing system as defined in claim 1 wherein the exterior of the electrode of smaller radius and the interior of the electrode of larger radius of each of said pairs of electrodes is coated with a low reflecting material for infrared radiation, a source of electrons for producing approximately a point source of electrons at a point midway between said first pair of conducting electrodes at the edges thereof and diametrically opposite said point of said line, and an infrared target mounted between the electrodes of said second pair of electrodes at the edges thereof in a region diametrically opposite said point of said line.

3*. An electrostatic deflection and focusing system comprising a first pair of quarter-sphere conducting electrodes of different radii mounted concentrically to subtend substantially the same solid angle, a second pair of quarten.

sphere conducting electrodes of different radii mounted concentrically to subtend substantially the same solid angle, said two pairs of electrodes being mounted in opposed adjacent relationship such that a bisecting plane of said first pair of electrodes orthogonally intersects a bisecting plane of said second pair of electrodes along a line that has apoint approximately midway between the electrodes of each pair at edges thereof.

4. An infrared camera tube comprising the deflection and focusing system as defined in claim 3 wherein the exterior of the electrode of smaller radius and the interior of the electrode of larger radius of each of said pairs, of electrodes is coated with a low reflecting material. for infrared radiation, a source of electrons for producing approximately a point source of electrons mid-- way between and at the edges of said first pair of conducting electrodes at a point opposite from said point of'said line, and an infrared target mounted between the electrodes, of said, second pair of electrodes at the edges thereof at a region opposite from said point of said line.

5. An electrostatic system for deflecting and focusing an electron beam comprising a first pair of spherical segment conducting electrodes of different radii mounted concentrically to subtend substantially the same solid angle, a second pair of spherical segment conducting electrodes. of different radii mounted concentrically to subtend substantially the same solid angle and in opposed relationship with said first pair of electrodes such that he center lines between the electrodes of each of said first and second pairs of electrodes are continuous, at

third pair of spherical 'segment conducting electrodes of different radii mounted concentrically to subtend substantially the same solid angle and in adjacent orthogonal relationship with said second pair of electrodes such that the center lines between the electrodes of each said second and third pairs of electrodes are continuous, and a fourth pair of spherical segment conducting electrodes of different radii mounted concentrically to subtend substantially the same solid angle in opposed adjacent relationship with said third pair of electrodes such that the center lines between the electrodes of each of said third and fourth pairs of electrodes are continuous.

6. An electrostatic system for deflecting and focusing an electron beam comprising a first pair of spherical segment conducting electrodes of different radii mounted concentrically to subtend substantially the same solid angle, and a second pair of spherical segment conducting electrodes of different radii mounted concentrically to subtend substantially the same solid angle, wherein said second pair of electrodes are in opposed adjacent relationship with said first pair of electrodes such that the center lines between the electrodes of each of said first and second pairs of electrodes are continuous.

7. An infrared camera tube comprising means for producing a flow of electrons of initial small cross-sectional area, an infrared target, and means for producing a spherical electrical field for deflecting said flow of electrons over a circuitous path and for focusing said flow of electrons to a small cross-sectional area on said target.

8. An electrostatic deflection and focusing system comprising a first pair of hollow hemispherically-shaped electrodes of different radii mounted concentrically one within the other to provide a space between said elec trodes for an electron beam path, a second pair of hollow hemispherically-shaped conducting electrodes of different radii mounted concentrically one within another to provide a space between the electrodes of said second pair for an electron beam path, said two pairs of electrodes being mounted in opposed adjacent relationship with adjoining spaces to provide a continuous electron beam path and such that bisecting planes of said two pairs of electrodes approximately orthogonally intersect along a line having a point between the electrodes of each of said pairs.

9. An electrostatic deflection and focusing system comprising a first pair of spherical segment electrodes of diiferent radii mounted concentrically one within another to provide a space between electrodes for an electron beam path, a second pair of spherical segment electrodes of different radii mounted concentrically one within another to provide a space between electrodes for an electron beam path, said two pairs of spherical segment electrodes mounted in opposed adjacent relationship with adjoining spaces to provide a continuous electron beam path and such that bisecting planes of said two pairs of spherical segment electrodes approximately orthogonally intersect along a line having a point between the electrodes of each of said pairs.

References Cited in the file of this patent UNITED STATES PATENTS Iams Sept. 16, 1941 

